I would agree to disagree here. Its ok that you skem the thing so bad that a machine can not read it but sometimes (more often than not), its obscured so bad that I have hard times reading it. I have to refresh the page 5-6 times to get a comprehensible image and proceed. May be I am a machine, may be I am a bot and may be its about time I got my eyesight checked?
There are arguments both in the favour and against the technology and since I hate CAPTCHA, I would tend to favour the ones against it ;)
A detailed discription can be found on Captcha and Wikipedia.

